Maths especially, the Sciences, English Literature, Languages and humanities like geography or history are generally considered good a levels that can give you a wide range of options (being facilitating subjects). That's because they give you a range of wanted skills like essay writing, general maths skills and knowledge of planning, etc.
If you have completely no idea (obviously it's your choice and others may think differently though) I would personally recommend Mathematics, a science and an essay based subject. If you want you could always do a science or something as an As level and then just do another a level that may interest you, say Product Design.
The reason I say that is because Maths is well respected always and leaves a wide range of routes from Economics to Computer Science. Essay based subjects are also respected for many jobs like Public Relations, Journalism etc. And with a science subject, if you prefer a science these also look good but leave a range of options - e.g. Biology could lead to ecology, conservation, working with animals.
This is notably dependent on your feelings, but this combination gives a wide range of options while also looking good for the future, giving you many skills and such.
If you want to find out more about subjects you can always do virtual work experience with SpringPod, or do some MOOCs to get an idea of what higher level learning in a subject is like? That might help you find a passion.
It's hard to say if there's any jobs as that really requires experimenting, like with what I just mentioned.
I hope this helped! Others will give their own thoughts that you can also consider, and in the end it's up to you, but this is definitely what I would call a base blueprint if you don't know what to do. Best of luck with whatever you do